Technique and blade arrangement to reduce the serpentine motion of a mass particle flowing through a turbomachine

ABSTRACT

An axial-flow turbo-machine where, in order to reduce serpentine motion of the mass particles of the working medium in flowing through the machine, the fixed and movable blades are shaped in such manner that radial forces are induced in the working medium which compensate, at least in part, the radial forces resulting from the peripheral component of the flow velocity which are responsible for the serpentine motion.

United States Patent 1191 Dzung Oct. 9, 1973 [54] TECHNIQUE AND BLADEARRANGEMENT 3,045,969 7/1962 Meienberg 415/119 o REDUCE THE SERPENTINEMOTION 2,298,576 10/1942 McElroy et a1. 415/191 2,224,519 12/1940McIntyre 415/192 OF A MASS PARTICLE FLOWING 2,320,733 6/1943 McIntyre415/192 THROUGH A TURBOMACHINE [75] Inventor: Lang Shuen Dzung,Wettingen, FOREIGN PATENTS OR APPLICATIONS Switzerland 631,231 10/1949Great Britain 415/210 311,606 3/1919 Germany .1 AssigneeiAktiengesellschaft r B ri & 722,001 1/1955 Great Britain 415 193 Co.,Baden, Switzerland [22] Filed: Apr. 30, 1971 Primary Examiner1-1enry F.Raduazo [21] pp o 39,0 Att0rneyPierce, Scheffler & Parker [30] ForeignApplication Priority Data [57] ABSTRACT May 27, 1970 Switzerland 7241/70axial'flow turbo'machine Where in to duce serpentine motion of the massparticles of the 52 U.S. c1. 415/193, 415/199 R WOrkinE medium inflowing through the machine, the [51] o 1/04 fixed and movable bladesare shaped in such manner [58] Field of Search 415/191, 192, 193, thatradial forces are induced in the Working medium 415/194, 195 199, 213 C210 119 which compensate, at least in part, the radial forces resultingfrom the peripheral component of the flow [56] References Cited velocitywhich are responsible for the serpentine mo- UNITED STATES PATENTS3,270,953 9/1966 Jerie et a1. 415/119 1 Claim, 5 Drawing FiguresTECHNIQUE AND BLADE ARRANGEMENT TO REDUCE THE SERPENTINE MOTION OF AMASS PARTICLE FLOWING THROUGH A TURBOMACHINE The present inventionrelates to an improved technique for reducing the serpentine motion,caused by the alternating peripheral component of the flow velocity, ofthe path, projected cylindrically on a meridional plane, of a massparticle in an axial-flow turbomachine, by means of the blading of themachine, and a blade arrangement to effect this technique.

In the blading of an axial-flow turbomachine, the flow medium issubjected to a serpentine motion in the meridional plane owing toperiodic variation of the peripheral component of the flow velocity andto the associated variation of the centrifugal forces. This serpentinemotion gives rise to additional energy losses and, by affecting the flowapproach angles, makes correct determination of the blade profilesdifficult.

A well-known countermeasure consists in twisting the blades so that theflow is free from eddies, at least in the axial direction. An eddy-freeflow can satisfy the condition of radial equilibrium without serpentinemotion. The disadvantage of this feature is that with machines of highvolume through-put, and hence large blade-diameter ratios, the bladeshave to be very sharply twisted. This increases manufacturing costs andfor reasons of strength is not always practicable.

Attempts have also been made to set the blades obliquely, relative tothe radial direction. The radial forces were meant to compensate thecentrifugal forces; this feature proved ineffective.

The purpose of the present invention is to reduce the serpentine motionof the working medium on its way through the turbo-machine, and also theenergy losses thus caused. In accordance with the invention this isachieved by making the blades of such a shape that radial forces areinduced in the working medium which at least partially compensate theradial forces resulting from the peripheral component.

A blade arrangement achieving this purpose is characterized by the factthat, when viewed in the axial direction and considered from base to tipof the blade, the leading and trailing edges of each fixed bladeconverge to at least such an extent that they coincide with a radius,and the leading and trailing edges of each moving blade, also viewed inthe axial direction and considered from base to tip of the blade,deviate from the radii passing through the base points of the leadingand trailing edges to at least such an extent that they areapproximately parallel or even somewhat convergent.

The invention is further explained below with the aid of the appendeddrawings. These show:

FIG. 1 different forms of fixed and moving blades, viewed in thedirection of the axis of the turbomachine,

FIG. 2 plane representation of part of cylindrical section II-II of FIG.1, through one row each of fixed and moving blades,

FIG. 3-5 associated flow diagrams.

To aid understanding of the invention, the cause of the serpentinemotion of a mass particle must be examined more closely. Consider atypical stage of a multiple-stage, axial-flow turbo-machine with 50percent reaction along the radius (i.e., the fixed and moving bladeseach convert one half of the stage drop). In front of the fixed row ofthe stage, the peripheral component of the flow velocity has a certainvalue which is first considered arbitrarily to be in a negativedirection. Within the blades of the fixed row the peripheral componentof this negative value increases to a certain new, positive value. Onflowing through the blades of the moving row the absolute peripheralcomponent of velocity is converted into work in accordance with Eulersturbine law. On leaving the moving row, this component again has thesame negative value as in front of the fixed row, whereupon this processis repeated in the next stage. This variation of the peripheralcomponent causes corresponding variation of the radial accelerationwhich, with constant reaction, is proportional to this velocitycomponent. The radial acceleration in turn gives rise to a radialcomponent of velocity, and hence to radial compression of thestreamlines in the meridional plane. This is the phenomenon ofserpentine motion.

FIG. 1 and 2 show a fixed blade 1 of a turbomachine with leading edge 3and trailing edge 4, and also a mov ing blade 2 with leading edge 5 andtrailing edge 6. The leading and trailing edges of both blades coincidewith radii, i.e., lines passing, through centre 0.

Curve 21 in FIG. 3 represents schematically the radial acceleration of amass particle in a stage as caused by the radial forces resulting fromthe peripheral component of the flow velocity. Curve 22 illustrates thevelocity, and curve 23 the radial displacement, where in each case, asalso in FIG. 4 and 5, the left-hand half of a diagram representsconditions in the fixed row, and the right-hand half conditions in themoving row of a stage. The abscissae are in each case the time taken bya mass particle of the working medium to flow through the stage. Exceptfor the influence of the constriction due to the blade thickness, thistime is proportional to the axial distance, so that curve 23 alsorepresents the meridional streamline projected cylindrically in ameridional plane. Curves 22 and 23 are obtained by single and doubleintegration, respectively, of curve 21, with the aid of suitableintegration constants. The above statements require modification ifaccount is taken of the finite thickness of the blade.

If all the blades could be made radial, as blades 1 and 2 in FIG. 1,then, apart from the radial acceleration caused by the flow processdescribed above, no radial blade force could be applied to the workingmedium. The traditional form of fixed and moving blades, however, iscylindrical, i.e., with practically parallel leading edges, as fixedblade 7 and moving blade 8 in FIG. 1. The leading and trailing edgesthen make the angle iv with the radii passing through their base points,such that the leading edge 9 of fixed blade 7 and the trailing edge 12of moving blade 8 form negative angles, while the trailing edge 10 offixed blade 7 and the leading edge 11 of moving blade 8 form positiveangles, as is shown for moving blade 8, with base points 13 and 14 forleading edge 11 and trailing edge 12, respectively. These angles 7 areat the same time the angles between the radial and peripheral componentsof the forces exerted by the blades on the working medium. Since theperipheral components of the flow velocity in the fixed and movingblades are always in mutually opposed directions, the additional radialblade-force components in the fixed and moving blades, and hence alsothe additional radial accelerations, always follow a similar course,e.g. as curve 31 in FIG. 4. Integration of curve 31 again yieldsvelocity curve 32 and displacement curve 33.

Comparison of FIG. 3 and 4 shows that the radial forces in the fixedblades are added to each other, although they compensate each other in'the moving blades. This applies to both a turbine and a compressor. Asin the case of an oscillation of different frequencies the two causescannot cancel out each other. Indeed, the dissipation loss will alwaysbe cumulative.

In accordance with the invention, the fixed blades are so formed thattheir leading edges and trailing edges are essentially radial asindicated by blade I in FIG. 1 so that there are no radial forces actingon the fluid. The moving blades, e.g., blade 8 in FIG. 1, are so formedthat the leading edges, e.g., edge 11, are inclined at a positive angleof y with respect to the radial line so that the concave side of eachblade, i.e., the pressure side, as represented by the left-hand side ofthe moving blade in FIG. 2 is slightly facing toward the axis, while thetrailing edge, e.g., edge 12 of blade 8 is inclined at an opposite,i.e., a negative angle of 7 against the radial line. In this way, thereexists a component of force acting by the moving blades on the flowingfluid in the direction towards the center at the entrance and away fromthe center at the outlet. Curve 41 in FIG. shows these forces acting onthe fluid or the acceleration within the stage. By the accelerationwithin the stage. By comparing with FIG. 3 it is evident that the radialforces due to the peripheral component of the flow velocity and to theshape of the blading compensate each other in the moving blades, butthat no additional disturbing force occurs in the fixed blades.Integration with the appropriate integration constants yields curve 42for the velocity and curve 43 for the displacement. Comparison of curve43 with curve 23 of FIG. 3 shows that suitable choice of therelationship between the two causes of radial displacement results invery effective compensation.

The effect of compensation can be increased if the leading and trailingedges of the moving blades viewed in the axial direction and consideredfrom base to tip of the blade converge as shown by in FIG. 1. In thisway the relationship between the two causes of radial displacement of amass particle can be altered. It must be expressly emphasized here thatthis blade form is not to be confused with the well-known technique oftapering the blades. This is, as a rule, such that in axial section theblades are indeed broader at the base than at the tip, but that therelationships in the peripheral direction are reversed.

Also in the case of the fixed blades a compensating force can be appliedif the leading and trailing edges, considered from base to tip of theblade, are inclined towards each other even more than the correspondingradii, e.g., as 16 in FIG. 1. If the radial force in the fixed bladesacts in the appropriate direction, almost com plete compensation can beachieved.

A similar increase in effectiveness can be achieved with a bladearrangement in accordance with the invention such that the moving bladesare broader than the fixed blades in either the peripheral direction orthe axial direction. As comparison between FIGS. 3 and 5 has shown, acompensating effect occurs only in the case of the moving blades. Whenthe moving row is wider in the axial direction, the time taken inflowing through the moving blades is greater; the same radialacceleration then gives rise to a higher value of the radial velocityand of the radial displacement. If the moving blades are broader in theperipheral direction, the value of angle 1 'y in FIG. 1 is higher, thusreinforcing the compensating effect.

I claim:

1. A multi-stage axial-flow turbo-machine, each stage thereof comprisinga row of fixed blades having a concave curved configuration and anadjacent row of movable blades having an oppositely concave curvedconfiguration, the leading and trailing edges of said fixed blades ofeach stage extending along radial lines as viewed in the direction ofthe axis, the leading edges of said movable blades of each stage beinginclined at a positive angle with respect to a radial line whereby theconcave side of each movable blade faces slightly towards the axis, andthe trailing edges of said movable blades of each stage being inclinedat the same but negative angle with respect to a radial line, thereby toeffect a reduction in the serpentine motion of a mass particle as itpasses through successive stages of said multistage turbo-machine andwhich is caused by the alternating peripheral component of the flowvelocity of the particle path projected cylindrically on a meridonal

1. A multi-stage axial-flow turbo-machine, each stage thereof comprisinga row of fixed blades having a concave curved configuration and anadjacent row oF movable blades having an oppositely concave curvedconfiguration, the leading and trailing edges of said fixed blades ofeach stage extending along radial lines as viewed in the direction ofthe axis, the leading edges of said movable blades of each stage beinginclined at a positive angle with respect to a radial line whereby theconcave side of each movable blade faces slightly towards the axis, andthe trailing edges of said movable blades of each stage being inclinedat the same but negative angle with respect to a radial line, thereby toeffect a reduction in the serpentine motion of a mass particle as itpasses through successive stages of said multi-stage turbo-machine andwhich is caused by the alternating peripheral component of the flowvelocity of the particle path projected cylindrically on a meridonalplane.